Shoulder instability (SI) occurs when the soft tissues (joint capsule, ligaments, and labrum) that hold the humerus in the shallow ball-and-socket glenohumeral joint become stretched, torn, or detached. When these tissues are damaged, the resulting shoulder instability is characterized as structural. If instability is caused by abnormal muscle activity that places too much or too little stress on the shoulder joint, the condition is described as functional instability.

In teenagers and young adults, shoulder instability is typically the functional variety, and it can affect up to 2.6% of this population. The most common variety of functional SI among these individuals is posterior positional functional shoulder instability (PP-FSI).

Patients with PP-FSI experience disabling shoulder pain during mid-range movement of the shoulder joint, caused by a muscle imbalance where the external rotator cuff muscles and the posterior deltoid are under-active and the internal rotator muscles are hyperactive. There is also an altered balance of the periscapular muscles. Using functional MRI, researchers have observed that the brain of a PP-FSI patient may send abnormal signals to the shoulder muscles during movement, similar to an infant who hasn’t developed fine motor skills or a recovering stroke or brain injury patient.

The conservative treatment approach to PP-FSI involves manual therapies to help restore proper motion to the shoulder joint, specific exercises to strengthen the muscles that have become inactive, ice and nutritional recommendations to address inflammation, modalities like electronic muscle stimulation to retrain the muscles, and activity modifications to reduce the risk of re-injury during the initial phase of the healing process. Over time, the patient can begin to resume their normal activities, provided movement doesn’t lead to sharp, lancinating pain in the shoulder.

Other musculoskeletal injuries in the shoulder, arm, neck, or upper back that may have preceding or developed following the PP-FSI injury will also need to be addressed in order to return the patient to their normal activities.

While surgical intervention may be advised as a first course of treatment for some PP-FSI patients, treatment guidelines typically recommend utilizing non-surgical methods first, of which chiropractic care is an excellent choice.